Waste water is transported through a system of conduits, known as sewers, from the point of generation to a remote treatment or disposal site. Frequently, the exposed surfaces become deteriorated, resulting in undesirable leakage and difficulty with the flow of the fluid. The sewers are typically provided with a vertically disposed manhole. The manhole has an opening at the surface or grade level. The lower or invert end of the manhole has a flow path, known as a lateral, through which sewage flows on its way to the treatment plant. The manhole may be formed of cement, concrete or brick, and typically has an internal diameter many times greater than the diameter of the flow path of the lateral.
The sewage may generate an atmosphere which is damaging to the mortar with which a brick manhole is formed. Alternatively, the environment may be damaging to the cementitous material used in manufacturing the manhole. Should the manhole be damaged, then rainfall or surface water may enter the manhole, thereby overloading the sewage system and potentially causing untreated sewage to be discharged into streams, lakes, and the like. Preserving the structural integrity of manholes is one means of minimizing the load applied to a sewage pumping treatment plant. These problems also apply to sewage stations, which are located along the sewage collection system, and which may also require rehabilitation.
In the past, systems have been developed to rehabilitate or repair damaged manholes. For instance, my prior U.S. Pat. No. 5,265,981, the disclosure of which is incorporated herein by reference, discloses a system and method for rehabilitating a manhole. In that system, inner and outer fiberglass plies sandwich a middle impermeable ply. The outer ply is adapted for being impregnated with a material which rigidifies the outer ply to the manhole. The middle ply is impermeable and prevents fluid from seeping into the manhole. The inner layer is also impregnated with a material which rigidifies the inner layer, so that the manhole becomes structurally reinforced. My prior U.S. Pat. No. 5,490,744, the disclosure of which is incorporated herein by reference, discloses a method and apparatus for inflating and curing a resin impregnated manhole liner.
My above described patents constituted a significant and advantageous improvement in the art. However, further improvement is virtually always possible in any field of endeavor, which turned out to be true here. For example, because the middle ply is made from an impermeable material, it is slick and may not always bond well to the epoxy impregnated inner and outer plies. Thus, while the manhole is structurally reinforced, there still remains a risk of the inner reinforced layer prying loose.
Thus, there is a need in the art for a liner for sealing and reinforcing a manhole, in which an impermeable middle layer is structurally bonded with the inner and outer plies, providing extra structural reinforcement.